1. Field of the Invention
The present invention relates to a grid interconnection device connected to a power distribution system through which alternating-current power is transmitted and to a power supply device provided to a customer, to a grid interconnection system, and to a power control system.
2. Description of the Related Art
A number of customers (for example, houses or plants) are increasing, which are provided with alternating-current power from a substation have their own power generation devices (for example, solar power generation systems).
Specifically, a plurality of power distribution systems (hereinafter referred to as banks) are provided under a substation, and each bank has customers having their own power generation devices. Here, electric power generated by the power generation devices is not only consumed by power consumption devices (for example, home electric appliances) provided to the customers but may also be transmitted to other customers (i.e., to the bank side). A system that connects power generation devices and a bank to supply electric power to each other as described above is referred to as a grid interconnection system.
In the grid interconnection system, when transmission of alternating-current power from a substation is stopped, for example, when a power failure occurs, power system separate processing for separating the power generation devices from the bank is carried out. On the other hand, when transmission of alternating-current power from a substation is started, for example, when the power failure is restored, grid interconnection processing for connecting the power generation devices to the bank is carried out.
Here, as a method for detecting that the transmission of alternating-current power is stopped (or that the transmission thereof is restored), there has been known a method that monitors, on the customer side, a state of alternating-current power to be transmitted through the bank. Specifically, the customer detects that the transmission of alternating-current power is stopped (or that the transmission thereof is restored) through monitoring data such as a change in voltage, or a change in phase of the voltage or a change in frequency, with regard to the alternating-current power transmitted through the bank.
In addition, there has been proposed a technique in which an operator of a power company or the like transmits, to the customers through wireless communication, a signal instructing the customers to stop their power generation devices (see, for example, Japanese Patent No. 3240215 (claim 1, paragraph [0019], FIG. 1, and the like)).
Specifically, the operator transmits, through wireless communication, area information specifying an area to be instructed to stop the power generation devices. Then, the customers determine whether to stop the power generation devices depending on whether they are included in the area specified by the area information.
Of the electric power generated by the power generation devices, an electric power amount to be transmitted to the bank is generally controlled based on standards predetermined by the guideline in order to prevent an excessive load from being applied on a power transmission line.
In the case where the transmission of alternating-current power is restored after the transmission of alternating-current power is stopped, the customers start interconnecting their power generation devices to the bank all at once. If numbers of the power generation devices start the grid interconnection all at once, a voltage of the bank rises so sharply that it becomes out of the control carried out based on the standards predetermined by the guideline. Consequently, the electric power amount to be transmitted to the bank could temporarily become excessively large.
That is to say, it is likely that an excessive load is applied on the power transmission line by the electric power to be transmitted from the customers to the bank in a case where the transmission of alternating-current power is restored.